The present invention relates to an extracting device that uses the flow of the liquid through a hydraulic system for removing grit or other particles from a solid-laden liquid.
A known grit extractor apparatus for liquid sewage includes inlet and outlet troughs or flumes connected to a round settling chamber. This type of apparatus has a typical flow rate turn down ratio of about four to one.
In the known grit extractor apparatus, flow velocity is a critical factor in determining turn down ratio. The flow velocity must be maintained between about 1.5 feet per second to about 3.5 feet per second. A flow velocity below 1.5 feet per second will tend to allow grit to settle in the extractor troughs where it is difficult to remove by the flow stream. As a result, the troughs have to be manually cleaned. For a flow velocity above 1.5 feet per second, the flow is turbulent. When the flow is too turbulent, at velocity above 3.5 feet per second, the grit will not move to the bottom of the flow stream where it can effectively attach to the bottom of the chamber, and will not remain on the bottom of the chamber to be moved to a central grit storage chamber.
Grit extractor apparatus are disclosed in U.S. Pat. Nos. 4,767,532; 4,107,038; and 3,941,698. The grit extractor apparatus of these patents introduce the liquid and grit into a round chamber wherein the resultant hydraulics within the chamber control the degree of grit removal. There is a natural tendency in these extractor apparatus for the hydraulic flow to pass from the influent to the effluent as rapidly as possible. This tendency results in some short circuiting across the chamber, especially at low flows, resulting in less than optimum grit removal. The effluent flow from the round chamber is over a broad area. The outflow has a large radial vector that results in decreasing the circular velocity, due to being at right angles to the circular flow. Reduced circular velocity can result in inefficient velocity to move grit, causing grit buildup on the floor of the chamber, especially at low liquid flow rates.
There is little control of liquid flow velocity entering the chamber, as flow velocity is a function of flume width, which is a set dimension, the quantity of liquid flowing, and the height of the liquid flowing in the flume. If the velocity is too great, the grit is uniformly suspended or distributed in the flow. Uniform distributed grit is harder to recover. If the level in the inlet or influent flume is raised, by elevating the level of the outlet or effluent flume, the velocity at low flows will be low and cause grit accumulation in the chamber or in the influent flume. Because of these design restraints, a typical four to one turn down ratio is a design limitation.
The present inventors have recognized the desirability of providing a grit extractor apparatus that is designed for future anticipated higher flow rates, and yet be able to effectively operate for present day smaller flow rates. For example, if a difference in daily peak flow to minimum daily flow is about three to one to four to one, it is understandable that a future peak or maximum flow rate incorporated into a design may be projected to a larger amount, such as twice as large as the present maximum flow rate, such that the turn down ratio from the present minimum flows to the future maximum or peak flows will be six to one to eight to one.
The present inventors have recognized the desirability of reducing the area or xe2x80x9cfootprintxe2x80x9d of such extractor apparatus to fit the apparatus inside existing buildings, to install larger extractor apparatus in the same space that an existing extractor apparatus occupies, or in order to minimize space in a new plant.
A grit extractor apparatus according to the present invention achieves optimum grit removal by using hydraulic currents to rotate grit-laden liquid so the grit comes in contact with the bottom of the grit removal chamber at a sufficiently slow velocity to be deposited on the bottom. The velocity is sufficiently fast such that hydraulic currents generate a moving force that gently pushes the grit along the floor of the chamber to the center where the grit is collected in a storage chamber for removal.
The present invention incorporates novel structure to control the flow of liquid and grit within a circular chamber and within inlet and outlet troughs or flumes. The flow velocity entering and leaving the chamber is controlled by the width of the entrance of the outlet flume. The velocity is controlled over a ten to one flow range by the novel use of hydraulic phenomena of the fluid level entering a narrow flume. According to the present invention, a ten to one variation in flow is achieved with an effective flow velocity in the range of 1.5 feet per second to 3.5 feet per second.
Hydraulic control of flow velocity is incorporated inside of the grit chamber instead of outside of the chamber, as in existing grit removal devices. This feature reduces the area that the unit occupies and greatly reduces the installation footprint. The grit extractor apparatus of the invention increases efficiency of grit removal.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.